1. Field of the Invention
The present invention generally concerns optical tweezers, microfluidics, flow cytometry, biological Micro Optical Electro Mechanical Systems (Bio-MOEMS), Laguerre-Gaussian mode emissions from Vertical Cavity Surface Emitting Lasers (VCSELs), cell cytometry and microfluidic switches and switching.
The present invention particularly concerns the sorting of microparticles in fluid, thus a xe2x80x9cmicrofluidic sorting devicexe2x80x9d; and also the directed movement, particularly for purposes of switching, of microparticles based on the transference of momentum from photons impinging on the microparticles, ergo xe2x80x9cphotonic momentum transferxe2x80x9d.
2. Description of the Prior Art
2.1 Background to the Functionality of the Present Invention
In the last several years much attention has been paid to the potential for lab-on-a-chip devices to significantly enhance the speed of biological and medical research and discovery. See P. Swanson, R. Gelbart, E. Atlas. L. Yang, T. Grogan, W. F. Butler, D. E. Ackley, and C. Sheldon. xe2x80x9cA fully multiplexed CMOS biochip for DNA analysis,xe2x80x9d Sensors and Actuators B 64, 22-30 (2000). See also M. Ozkan, C. S. Ozkan, M. M. Wang, O. Kibar, S. Bhatia, and S. C. Esener, xe2x80x9cHeterogeneous Integration of Biological Species and Inorganic Objects by Electrokinetic Movement,xe2x80x9d IEEE Engineering in Medicine and Biology, in press.
The advantages of such bio-chips that have been demonstrated so far include the abilities to operate with extremely small sample volumes (on the order of nanoliters) and to perform analyses at much higher rates than can be achieved by traditional methods. Devices for study of objects as small as DNA molecules to as large as living cells have been demonstrated. See P. C. H. Li and D J, Harrison, Transport, Manipulation, and Reaction of Biological Cells On-Chip Using Electrokinetic Effects,xe2x80x9d Anal. Chem. 69, 1564-1569 (1997).
One important capability for cell research is the ability to perform cell sorting, or cytometry, based on the type, size, or function of a cell. Recent approaches to micro-cytometry have been based on electrophoretic or electro-osmotic separation of different cell types. See A. Y. Fu, C. Spence, A. Scherer, F. H. Arnold, and S. R Quake, xe2x80x9cA microfabricated fluorescence-activated cell sorter,xe2x80x9d Nature 17.1109-1111 (1999).
2.2 Scientific Background to the Structure of the Device of the Present Invention
The present invention will be seen to employ optical tweezers. See A. Ashkin, J. M. Dziedzic, J. E. Bjorkholm, and S. Chu, xe2x80x9cObservation of a single-beam gradient force optical trap for dielectric particles;xe2x80x9d Opt. Lett. 11, 288-291) (1986).
The present invention will also be seen to employ micro-fabricated fluidic channels. See H. -P. Chou, C. Spence. A. Scherer. and S. Quake, xe2x80x9cA microfabricated device for sizing and sorting DNA molecules,xe2x80x9d Proc. Natl. Acad. Sci. USA 96 11-13 (1999).
In previous demonstrations of the optical manipulation of objects through defined fluidic channels, photonic pressure was used to transport cells over the length of the channels. See T. N. Buican M. J. Smyth, H. A. Crissman, G. C. Salzman, C. C. Stewart, and J. C. Martin, xe2x80x9cAutomated single-cell manipulation and sorting by light trapping.xe2x80x9d Appl. Opt, 26, 3311-5316 (1987). The device of the present invention will be seen to function oppositely.
2.3 Engineering, and Patent, Background to the Structure of the Device of the Present Invention
There are many existing (i) bio-chip (lab-on-a-chip) technologies, and (ii) microfluidic technologies. Most of these technologies use electrical or mechanical force to perform switching within the channels. The present invention is unique in that optics (as generate photonic pressure, or radiation pressure) is used to perform switchingxe2x80x94particularly of small particles flowing in microfluidic channels.
2.3.1 Background Patents Generally Concerning Optical Tweezing and Optical Particle Manipulation
The concept of using photonic pressure to move small particles is known. The following patents, all to Ashkin, generally deal with Optical Tweezers. They all describe the use of optical xe2x80x9cpushingxe2x80x9d and optical xe2x80x9ctrappingxe2x80x9d forces, both of which are used in the present invention. These patents do not, however, teach or suggest such use of optical forces in combination with microfluidics as will be seen to be the essence of the present invention.
U.S. Pat. No. 3,710,279 to Askin, assigned to Bell Telephone Laboratories, Inc. (Murray Hill, N.J.), for APPARATUSES FOR TRAPPING AND ACCELERATING NEUTRAL PARTICLES concerns a variety apparatus for controlling by radiation pressure the motion of particle, such as a neutral biological particle, free to move with respect to its environment. A subsequent Askin patent resulting from a continuation-in-part application is U.S. Pat. No. 3,808,550.
Finally, U.S. Pat. No. 4,893,886 again to Ashkin, et al., assigned to American Telephone and Telegraph Company (New York, N.Y.) and ATandT Bell Laboratories (Murray Hill, N.J.), for a NON-DESTRUCTIVE OPTICAL TRAP FOR BIOLOGICAL PARTICLES AND METHOD OF DOING SAME, concerns biological particles successfully trapped in a single-beam gradient force trap by use of an infrared laser. The high numerical aperture lens objective in the trap is also used for simultaneous viewing. Several modes of trapping operation are presented.
2.3.2 Patents Showing Various Conjunctions of Optical Tweezing/Optical Manipulation and Microfluidics/Microchannels
U.S. Pat. No. 4,887,721 to Martin, et al., assigned to Bell Telephone Laboratories, Inc. (Murray Hill, N.J.), for a LASER PARTICLE SORTER, concerns a method and apparatus for sorting particles, such as biological particles. A first laser defines an optical path having an intensity gradient which is effective to propel the particles along the path but which is sufficiently weak that the particles are not trapped in an axial direction. A probe laser beam interrogates the particles to identify predetermined phenotypical characteristics of the particles. A second laser beam intersects the driving first laser beam, wherein the second laser beam is activated by an output signal indicative of a predetermined characteristic. The second laser beam is switchable between a first intensity and a second intensity, where the first intensity is effective to displace selected particles from the driving laser beam and the second intensity is effective to propel selected particles along the deflection laser beam. The selected particles may then be propelled by the deflection beam to a location effective for further analysis.
The described particle propulsion means of Martin, et al. concerns (i) the suspension of particles by fluidics and (ii) the use of an optical pushing beam to move particles around in a cavity. The application of sortingxe2x80x94as is performed by certain apparatus of the present inventionxe2x80x94is also described. However, the present invention is distinguished over U.S. Pat. No. 4,887,721 for SORTING IN MICROFLUIDICS to Martin, et al. because this patent teaches the use of optical beams to do all particle transport, while the present invention uses optical beams only for switching, with transport accomplished by microfluidic flow. In the apparatus of U.S. Pat. No. 4,887,721 a single beam pushes a particle along from one chamber to the next. It will soon be seen that in the various apparatus of the present invention continuous water flow serves to move the particles around, and optics is only used as the switch. This is a much more efficient use of photons and makes for a faster throughput device.
The Martin, et al. patent also describes (i) sensing particles by optical means, and (ii) act on the results of the sensing so as to (iii) manipulate the particles with laser light. Such optical sensing is fully compatible with the present invention.
Also involving both (i) fluidics and, separately, (ii) optical manipulation is U.S. Pat. No. 5,674,743 to Ulmer, assigned to SEQ, Ltd. (Princeton, N.J.), for METHODS AND APPARATUS FOR DNA SEQUENCING. The Ulmer patent concerns a method and apparatus for automated DNA sequencing. The method of the invention includes the steps of: a) using a processive exonuclease to cleave from a single DNA strand the next available single nucleotide on the strand; b) transporting the single nucleotide away from the DNA strand; c) incorporating the single nucleotide in a fluorescence-enhancing matrix; d) irradiating the single nucleotide to cause it to fluoresce; e) detecting the fluorescence; f) identifying the single nucleotide by its fluorescence; and g) repeating steps a) to f) indefinitely (e.g., until the DNA strand is fully cleaved or until a desired length of the DNA is sequenced). The apparatus of the invention includes a cleaving station for the extraction of DNA from cells and the separation of single nucleotides from the DNA; a transport system to separate the single nucleotide from the DNA and incorporate the single nucleotide in a fluorescence-enhancing matrix; and a detection station for the irradiation, detection and identification of the single nucleotides. The nucleotides are advantageously detected by irradiating the nucleotides with a laser to stimulate their natural fluorescence, detecting the fluorescence spectrum and matching the detected spectrum with that previously recorded for the four nucleotides in order to identify the specific nucleotide.
In one embodiment of the Ulmer apparatus an electric field applied (about 0.1-10 V/cm) via suitably incorporated electrodes to induce the chromosomes to migrate into a microchannel single-file, much as is done in an initial step of cell sorting. The individual chromosomes are visualized by the microscope system as they proceed along the microchannel. This step can also be automated by using computer image analysis for the identification of chromosomes (see Zeidler, 1988, Nature 334:635). Bifurcations in the channel are similarly used in conjunction with selectively applied electric fields to divert the individual chromosomes into small isolation chambers. Once individual chromosomes have been isolated, the sister chromatids are separated by either a focused laser microbeam and optical tweezers, or mechanical microdissection to provide two xe2x80x9cidenticalxe2x80x9d copies for sequencing.
The present invention will be seen to use optical tweezers not only on chromosomes and the like once delivered to xe2x80x9cchambersxe2x80x9d by use of microchannels, but also to divert the particles within the microchannels themselvesxe2x80x94a process that Ulmer contemplates to do only by electric fields.
U.S. Pat. No. 5,495,105 to Nishimura, et al. for a METHOD AND APPARATUS FOR PARTICLE MANIPULATION, AND MEASURING APPARATUS UTILIZING THE SAME concerns a flow of liquid containing floating fine particles formed in a flow path, thereby causing successive movement of the particles. A light beam having intensity distribution from a laser is focused on the liquid flow, whereby the particle is optically trapped at the irradiating position, thus being stopped against the liquid flow or being slowed by a braking force. This phenomenon is utilized in controlling the spacing of the particles in the flow or in separating the particles.
The present invention will be seen not to be concerned with retarding (breaking) or trapping the flow of particles in a fluid, but rather in changing the path(s) of particle flow.
The next three patents discussed are not necessarily prior art to the present invention because they have issuance dates that are later than one year prior to the priority date of the present patent application as this priority date is established by the predecessor provisional patent application, referenced above. However, these patents are mentioned for completeness in describing the general current, circa 21001, state of the art in microfluidic and/or laser manipulative particle processing, and so that the distinction of the present invention over existing alternative techniques may be better understood.
In this regard, U.S. Pat. No. 6,139,831 to Shivashankar, et al., assigned to The Rockfeller University (New York, N.Y.), for an APPARATUS AND METHOD FOR IMMOBILIZING MOLECULES ONTO A SUBSTRATE, contemplates both (i) movement by microfluidics and (ii) manipulation by optical tweezers. However, Shivashankar, et al. contemplate that these should be separate events.
The Shivashankar, et al., patent concerns an apparatus and method for immobilizing molecules, particularly biomolecules such as DNA, RNA, proteins, lipids, carbohydrates, or hormones onto a substrate such as glass or silica. Patterns of immobilization can be made resulting in addressable, discrete arrays of molecules on a substrate, having applications in bioelectronics, DNA hybridization assays, drug assays, etc. The Shivashankar, et al., invention reportedly readily permits grafting arrays of genomic DNA and proteins for real-time process monitoring based on DNA-DNA, DNA-protein or receptor-ligand interactions. In the apparatus an optical tweezer is usable as a non-invasive tool, permitting a particle coated with a molecule, such as a bio-molecule, to be selected and grafted onto spatially localized positions of a semiconductor substrate. It is recognized that this non-invasive optical method, in addition to biochip fabrication, has applications in grafting arrays of specific biomolecules within microfluidic chambers, and it is forecast by Shivashankar, et al., that optical separation methods may work for molecules as well as cells.
Well they may; however the present invention will be seen, inter alia, to employ optical tweezers on biomolecules while moving these molecules move in microchannels under microfluidic forcesxe2x80x94as opposed to being stationary in microfluidic chambers.
U.S. Pat. No. 6,159,749 to Liu, assigned to Beckman Coulter, Inc. (Fullerton, Calif.), for a HIGHLY SENSITIVE BEAD-BASED MULTI-ANALYTE ASSAY SYSTEM USING OPTICAL TWEEZERS concerns an apparatus and method for chemical and biological analysis, the apparatus having an optical trapping means to manipulate the reaction substrate, and a measurement means. The optical trapping means is essentially a laser source capable of emitting a beam of suitable wavelength (e.g., Nd:YAG laser). The laser beam impinges upon a dielectric microparticle (e.g., a 5 micron polystyrene bead which serves as a reaction substrate), and the bead is thus confined at the focus of the laser beam by a radial component of the gradient force. Once xe2x80x9ctrapped,xe2x80x9d the bead can be moved, either by moving the beam focus, or by moving the reaction chamber. In this manner, the bead can be transferred among separate reaction wells connected by microchannels to permit reactions with the reagent affixed to the bead, and the reagents contained in the individual wells.
The patent of Liu thus describes the act of moving particlesxe2x80x94beadsxe2x80x94in microchannels under force of optical laser beams, or traps. However, as with the other references, Liu does not contemplate that particles moving under force of microfluidics should also be subject to optical forces.
U.S. Pat. No. 6,294,063 to Becker, et al., assigned to the Board of Regents, The University of Texas System (Austin, Tex.), for a METHOD AND APPARATUS FOR PROGRAMMABLE FLUIDIC PROCESSING concerns a method and apparatus for microfluidic processing by programmably manipulating a packet. A material is introduced onto a reaction surface and compartmentalized to form a packet. A position of the packet is sensed with a position sensor. A programmable manipulation force is applied to the packet at the position. The programmable manipulation force is adjustable according to packet position by a controller. The packet is programmably moved according to the programmable manipulation force along arbitrarily chosen paths.
It is contemplated that the xe2x80x9cpacketsxe2x80x9d may be moved along the xe2x80x9cpathsxe2x80x9d by many different types of forces including optical forces. The forces are described to be any of dielectrophoretic, electrophoretic, optical (as may arise, for example, through the use of optical tweezers), mechanical (as may arise, for example, from elastic traveling waves or from acoustic waves), or any other suitable type of force (or combination thereof). Then, in at least some embodiments, these forces are programmable. Using such programmable forces, packets may be manipulated along arbitrarily chosen paths.
As with the other described patents, the method and apparatus of Becker, et al., does not contemplate moving with one forcexe2x80x94microfluidicsxe2x80x94while manipulating with another forcexe2x80x94an optical force.
In one of its several aspects the present invention contemplates the use of optical beams (as generate photonic pressure, or radiation pressure) to perform switching of small particles that are flowing in microfluidic channels. The invention is particularly beneficial of use in bio-chip technologies where one wishes to both transport and sort cells (or other biological samples).
In its microfluidic switching aspect, the present invention contemplates the optical, or radiation, manipulation of microparticles within a continuous fluid, normally water, flowing through small, microfluidic, channels. The water flow may be induced by electro-osmosis, pressure, pumping, or whatever. A particle within a flowing fluid passes into a junction that is typically in the shape of an inverted xe2x80x9cTxe2x80x9d or xe2x80x9cYxe2x80x9d, or an xe2x80x9cXxe2x80x9d, or, more generally, any branching of n input channels where n=1, 2, 3, . . . N, to M output channels where m=1, 2, 3, . . . M. Photonic forces serve to controllably direct a particle appearing at the junction from one of the n input channels into (i.e., xe2x80x9cdown toxe2x80x9d) one of the m output channels. The photonic forces may be in the nature of pulling forces, or, more preferably, photonic pressure forces, or both pulling and pushing forces to controllably force the particle in the desired direction and into the desired output channel. Two or more lasers may be directionally opposed so that a particle appearing at one of the n input channels may be pushed (or pulled) in either direction to one of the m output channels.
The size range of the microfuidic channels is preferably from 2 xcexcm to 200 xcexcm in diameter, respectively switching and sorting microparticles, including living cells, in a size range from 1 xcexcm to 100 xcexcm in diameter.
This microfluidic switching aspect of the present invention has two major embodiments, which embodiments are more completely expounded in the DESCRIPTION OF THE PREFERRED EMBODIMENT of this specification as section 1 entitled xe2x80x9cAll-Optical Switching of Biological Samples in a Microfluidic Devicexe2x80x9d, and as section 2 entitled xe2x80x9cIntegration of Optoelectronic Array Devices for Cell Transport and Sorting. Furthermore, the xe2x80x9coptoelectronic array devicesxe2x80x9d of the second embodiment are most preferably implemented as the VCSEL tweezers, and these tweezers are more completely expounded in the section 3 entitled xe2x80x9cVCSEL Optical Tweezers, Including as Are Implemented as Arraysxe2x80x9d.
In a first embodiment of the microfluidic switching (expounded in section 1.) an optical tweezer trap is used to trap a particle as it enters the junction and to xe2x80x9cPULLxe2x80x9d it to one side or the other. In a second embodiment of the microfluidic switching (expounded in section 2.), the scattering force of an optical beam is used to xe2x80x9cPUSHxe2x80x9d a particle towards one output or the other. Both embodiments have been reduced to operative practice, and the choice of which embodiment to use, or to use both embodiments simultaneously, is a function of exactly what is being attempted to be maneuvered, and where. The xe2x80x9cPUSHxe2x80x9d solutionxe2x80x94which can, and preferably is, also based on a VCSEL, or VCSEL arrayxe2x80x94is generally more flexible and less expensive, but produces less strong forces, than the xe2x80x9cPULLxe2x80x9d embodiment.
The particle passes through the optical beam only briefly, and then continues down a selected channel continuously following the fluid. Microfluidic particle switches in accordance with the present invention can be made both (i) parallel and (ii) cascadablexe2x80x94which is a great advantage. A specific advantage of using optics for switching is that there is no physical contact with the particle, therefore concerns of cross-contamination are reduced.
Still another attribute of the invention is found within both specific embodiments where the optical switching beam preferably enters the switching region of a microfluidic chip orthogonally to the flat face of the chip. This means that the several microfluidic channels at the junction are at varying depths, or levels, in the chip, and the switching beams serve to force a particle transversely to the flat face of the chipxe2x80x94xe2x80x9cupxe2x80x9d or xe2x80x9cdownxe2x80x9d within the chipxe2x80x94to realize switching. Each optical beam is typically focused in a microfluidic junction by an external lens. This is very convenient, and eases optical design considerably. However, it will also be understood that optical beams could alternatively be entered by wave guides and/or microlenses fabricated directly within the microfluidic chip.
In another of its aspects, the present invention contemplates a new form of optical tweezer that is implemented from both (i) a Vertical Cavity Surface Emitting Laser (VCSEL) (or tweezer arrays that are implemented from arrayed VCSELs) and (ii) a VCSEL-light-transparent substrate in which are present microfluidic channels flowing fluid containing microparticles. The relatively low output power, and consequent relatively low optical trapping strength of a VCSEL, is in particular compensated for in the xe2x80x9cmicrofluidic optical tweezersxe2x80x9d of the present invention by changing the lasing, and laser light emission, mode of the VCSEL from Hermite-Gaussian to Laguerre Gaussian. This change is realized in accordance with the VCSEL post-fabrication annealing process taught within the related U.S. patent application, the contents of which are incorporated herein by reference.
The preferred VCSELs so annealed and so converted from a Hermite-Gaussian to a Laguerre-Gaussian emission mode emit light that is characterized by rotational symmetry and, in higher modal orders, close resembles the so-called xe2x80x9cdonutxe2x80x9d mode. Light of this characteristic is optimal for tweezing; the xe2x80x9ctweezedxe2x80x9d object is held within the center of a single laser beam. Meanwhile the ability to construct and to control arrayed VCSELs at low cost presents new opportunities for the sequenced control of tweezing and, in accordance with the present invention, the controlled transport and switching of microparticles traveling within microfluidic channels.
1. Moving and Manipulating Small Particles, Including for Switching and Sorting
Accordingly, in one of its aspects the present invention is embodied in a method of moving, and also manipulating, small particles, including for purposes of switching and sorting.
The method of both physically (i) moving and (ii) manipulating a small particle consists of (i) placing the particle in fluid flowing in a microfluidic channel; and (ii) manipulating the particle under force of radiation as it moves in the microfluidic channel.
The method may be extended and adapted to physically spatially switching the small particle to a selected one of plural alternative destination locations. In such case the placing of the particle in fluid flowing in a microfluidic channel consists of suspending the particle in fluid flowing in a compound microfluidic channel from (i) an upstream location through (ii) a junction branching to (iii) each of plural alternative downstream destination locations. The manipulating of the particle under force of radiation as it moves in the compound microfluidic channel then consists of controlling the particle at the branching junction to move under force of radiation into a selected path leading to a selected one of the plural alternative downstream destination locations.
The controlling is preferably with a single radiation beam, the particle being suspended within the flowing fluid passing straight through the junction into a path leading to a first downstream destination location in absence of the radiation beam. However, in the presence of the radiation beam the particle deflects into an alternative, second, downstream destination location.
The controlling may alternatively be with a selected one of two radiation beams impinging on the junction from different directions. The particle suspended within the flowing fluid deflects in one direction under radiation force of one radiation beam into a first path leading to a first downstream destination location. Alternatively, the particle deflects under radiation force of the other, different direction, radiation beam into a second path leading to a second downstream destination location.
In the case of generalized switching where a particle from any of n input paths is switched to any of m output paths, the particle will enter the junction from any number of n input paths that are normally spaced parallel, and will be deflected to a varying distance in either directions so as to enter a selected one of the m output paths. The particular radiation (laser) source that is energized, and the duration of the energization, will influence how far, and in what direction, the particle moves. Clearly forcing a particle to move a long distance, as when n or m or both are large numbers  greater than 4, entails (i) longer particle transit times with (ii) increasing error. Since particles can be sorted into large numbers (m greater than  greater than 4) of destinations in a cascade of microfluidic switches, no single switch is normally made excessively xe2x80x9cwidexe2x80x9d.
The controlling is preferably with a laser beam, and more preferably with a Vertical Cavity Surface Emitting (VCSEL) laser beam, and still more preferably with a VCSEL laser beam having Laguerre-Gaussian spatial energy distribution.
2. A Mechanism for Moving and Manipulating Small Particles, Including for Switching and Sorting
In another of its aspects the present invention is embodied in a mechanism for moving, and also manipulating, small particles, including for purposes of switching and sorting.
The preferred small particle moving and manipulating mechanism includes (i) a substrate in which is present at least one microfluidic channel, the substrate being radiation transparent at at least one region along the microfluidic channel; (ii) a flow inducer inducing a flow of fluid bearing small particles in the microfluidic channel; and (iii) at least one radiation beam selectively enabled to pass through at least one radiation-transparent region of the substrate and into the microfluidic channel so as to there produce a manipulating radiation force on the small particles as they flow by.
This small particles moving and manipulating mechanism according can be configured and adapted as a switching mechanism for sorting the small particles. In such case the substrate""s at least one microfluidic channel branches at the at least one junction. Meanwhile the flow inducer is inducing the flow of fluid bearing small particles in the at least one microfluidic channel including through the channel""s at least one junction and into all the channel""s branches. Still further meanwhile, the at least one radiation beam selectively passes through the radiation-transparent region of substrate and into a junction of the microfluidic channel so as to there selectively produce a radiation force on each small particle at such time as the particle should pass through the junction, which selective force will cause each small particle to enter into an associated desired one of the channel""s branches. By this coaction the small particles are controllably sorted into the channel branches.
In one variant embodiment, the substrate of the switch mechanism has plural levels differing in distance of separation from a major surface of the substrate The at least one microfluidic channel branches at the at least one junction between (i) at least one, first, path continuing on the same level and (ii) another, alternative second, path continuing on a different level. In operation one only radiation beam selectively acts on a small particle at the junction so as to (i) produce when ON a radiation force on the small particle at the junction that will cause the small particle to flow into the alternative second path. However, when this one radiation beam is OFF, the small particle will continue flowing upon the same level and into the first path.
3. A Small Particle Switch
In yet another of its aspects the present invention may simply be considered to be embodied in a small particle switch, or, more precisely, a switch mechanism for controllably spatially moving and switching a small particle arising from a particle source into a selected one of a plurality of particle sinks.
The switch includes a radiation-transparent microfluidic device defining a branched microfluidic channel, in which channel fluid containing a small particle can flow, proceeding from (i) particle source to (ii) a junction where the channel then branches into (iii) a plurality of paths respectively leading to the plurality of particle sinks. The switch also includes a flow inducer for inducing a flow of fluid, suitable to contain the small particle, in the microfluidic channel from the particle source through the junction to all the plurality of particle sinks. Finally, the switch includes at least one radiation beam selectively enabled to pass through the radiation-transparent microfluidic device and into the junction so as to there produce a radiation force on a small particle as it passes through the junction within the flow of fluid, therein by this selectively enabled and produced radiation force selectively directing the small particle that is within the fluid flow into a selected one of the plurality of paths, and to a selected one of the plurality of particle sinks.
In operation of the switch the small particle is physically transported in the microfluidic channel from the particle source to that particular particle sink where it ultimately goes by action of the flow of fluid within the microfluidic channel. The small particle is physically switched to a selected one of the plurality of microfluidic channel paths, and to a selected one of the plurality of particle sinks, by action of radiation force from the radiation beam.
The branched microfluidic channel of the radiation-transparent microfluidic device is typically bifurcated at the junction into two paths respectively leading to two particle sinks. The flow inducer thus induces the flow of fluid suitable to contain the small particle from the particle source through the junction to both particle sinks, while the at least one radiation beam is selectively enabled to produce a radiation force on a small particle as it passes through the junction within the flow of fluid so as to selectively direct the small particle into a selected one of the two paths, and to a selected one of the two particle sinks.
It is possible to use two radiation beams are selectively enabled to produce a radiation force on a small particle as it passes through the junction within the flow of fluid so as to selectively direct the small particle into a selected one of the two paths, and to a selected one of the two particle sinks, one of the two radiation beams being enabled to push the particle into one of the two paths and the other of the two radiation beams being enabled to push the particle into the other one of the two paths.
The preferred bifurcated junction splits into two paths one of which paths proceeds straight ahead and another of which paths veers away, the two paths respectively leading to two particle sinks. In this case preferably one radiation beam is selectively enabled to produce a radiation force on a small particle as it passes through the junction within the flow of fluid so as to push when enabled the small particle into the path that veers away, and so as to permit when not enabled that the particle will proceed in the path straight ahead.
When the bifurcated microfluidic channel of the radiation-transparent microfluidic device defines a geometric plane, then the one radiation beam is preferably substantially in the geometric plane at the junction.
4. Optical Tweezers
In still yet another of its aspects the present invention may simply be considered to be embodied in a new form of optical tweezers.
The optical tweezers have a body defining a microfluidic channel in which fluid transporting small particles flows, the body being transparent to radiation at at least some region of the microfluidic channel. A radiation source selectively acts, through the body at a radiation-transparent region thereof, on the transported small particles within the microfluidic channels. By this action the small particles (i) are transported by the fluid to a point of manipulation by the radiation source, and (ii) are there manipulated by the radiation source.
The radiation source preferably consists of one or more Vertical Cavity Surface Emitting Lasers (VCSELs), which may be arrayed in one, or in two dimensions as the number, and positions, of manipulating locations dictates.
The VCSEL radiation sources are preferably conditioned so as to emit laser light in the Laguerre-Gaussian mode, with a Laguerre-Gaussian spatial intensity distribution.
The one or more VCSELs are preferably disposed orthogonally to a surface, normally a major surface, of the body, normally a planar substrate, in which is present the microfluidic channel, laser light from at least one VCSEL, and normally all VCSELs, impinging substantially orthogonally on both the body and its microfluidic channel.
The microfluidic channel normally has a junction where an upstream, input, fluidic pathway bifurcates into at least two alternative, downstream, fluidic pathways. The presence or absence of the radiation at this junction then determines whether a particle contained within fluid flowing from the upstream fluidic pathway through the junction is induced to enter a one, or another, of the two alternative, downstream, fluidic pathways.
The two alternative, downstream, fluidic pathways of the microfluidic channel may be, and preferably are, separated in a xe2x80x9cZxe2x80x9d axis direction orthogonal to the plane of the substrate. The presence or absence of the laser light from the VCSEL at the junction thus selectively forces the particle in a xe2x80x9cZxe2x80x9d axis direction, orthogonal to the plane of the substrate, in order to determine which one of the two alternative, downstream, fluidic pathways the particle will enter.
However, the two alternative, downstream, fluidic pathways of the microfluidic channel may be separated in different directions in the plane of the substrate, the at least two alternative downstream, fluidic pathways then being of the topology of the arms of an inverted capital letter xe2x80x9cYxe2x80x9d, or, topologically equivalently, of the two opposing crossbar segments of an inverted capital letter xe2x80x9cTxe2x80x9d. The presence or absence of the laser light from the VCSEL at the junction then selectively forces the particle to deviate in direction of motion in the plane of the substrate, therein to determine which branch one of the two alternative, downstream, fluidic pathways the particle will enter.
5. An Optical Tweezing Method
In still yet another of its aspects the present invention may simply be considered to be embodied in a new method of optically tweezing a small particle.
The method consists of transporting the small particle in fluid flowing within a microfluidic channel, and then manipulating the small particle with laser light as it is transported by the flowing fluid within the channel.
The manipulating laser light is preferably from a Vertical Cavity Surface Emitting Laser (VCSEL), and still more preferably has a substantial Laguerre-Gaussian spatial energy distribution.
In the method a number of particles each in an associated microfluidic channel may each be illuminated in and by the laser light of an associated single Vertical Cavity Surface Emitting Lasers (VCSELs), all at the same time.
Alternatively, in the method multiple particles may be illuminated at multiple locations all within the same channel, and all at the same time.
The laser light illumination of the particle moving in the microfluidic channel under force of fluid flow is preferably substantially orthogonal to a local direction of the channel, and of the particle movement.
6. A Microfluidic Device
In still yet another of its aspects the present invention may be considered to be embodied in a microfluidic device for sorting a small particle within, and moving with, fluid flowing within microfluidic channels within the device.
The microfluidic device has a housing defining one or more microfluidic channels, in which channels fluid containing at least one small particle can flow, at least one microfluidic channel having at least one junction, said junction being a place where a small particle that is within a fluid flow proceeding from (i) a location within a microfluidic channel upstream of the junction, through (ii) the junction to (iii) a one of at least two different, alternative, microfluidic channels downstream of the junction, may be induced to enter into a selected one of the two downstream channels.
The device further has a flow inducer for inducing an upstream-to-downstream flow of fluid containing the at least one small particle in the microfluidic channels of the housing and through the junction.
Finally, the device has a source of optical, or photonic, forces for selectively producing photonic forces on the at least one small particle as it flows through the junction so as to controllably direct this at least one small particle that is within the fluid flow into a selected one of at the least two downstream microfluidic channels.
By this coaction the at least one small particle is transported from upstream to downstream in microfluidic channels by the flow of fluid within these channels, while the same small particle is sorted to a selected downstream microfluidic channel under a photonic force.
As before, a junction where sorting is realized may be in the topological shape of an inverted xe2x80x9cYxe2x80x9d or, topologically equivalently, a xe2x80x9cTxe2x80x9d, where a stem of the xe2x80x9cYxe2x80x9d, or of the xe2x80x9cTxe2x80x9d, is the upstream microfluidic channel, and where two legs of the xe2x80x9cYxe2x80x9d, or, topologically equivalently, two segments of the crossbar of the xe2x80x9cTxe2x80x9d, are two downstream microfluidic channels. Alternatively, a junction where sorting is realized may be in the shape of an xe2x80x9cXxe2x80x9d, where two legs of the xe2x80x9cXxe2x80x9d are upstream microfluidic channels, and where a remaining two legs of the xe2x80x9cXxe2x80x9d are two downstream microfluidic channels.
In all configurations the photonic pressure force pushes the at least one small particle in a selected direction.
These and other aspects and attributes of the present invention will become increasingly clear upon reference to the following drawings and accompanying specification.